Portrait of a black hole

Black holes represent the wonder and mystery of modern astronomy. These sinkholes in space have inspired a whole new field of deep-space research.

Nothing, not even light rays, can escape the gravitational clutches of black holes. They are deformities in the spacetime continuum and are created by highly compact masses and then fed by cosmic debris for millions, even billions of years.

If humans could travel down a black hole (not really very likely despite sci-fi tales to the contrary), they'd end up-where? No one really knows. What's inside these black holes? Do they emerge somewhere-or somewhen-else? If we ever know for sure, it will be thanks to mathematics and observation. The super gravity field lines and extreme cosmic radiations around these holes would obliterate all life, so we're not likely to ever get too close to these weird objects.

This year began a complex effort by the Harvard-Smithsonian Center for Astrophysics to electronically link dozens of radio astronomical observatories around the world to perform a very daring task-photograph a black hole for the first time in history.

When completed around the year 2020, the proposed Event Horizon Telescope, or EHT, will span our globe using a process called Very Long Baseline Interferometry. VLBI enables simultaneous observations of deep-space objects by multiple telescopes. In the case of the EHT project now underway, the radio telescopes are being combined to create a single, giant telescope on Earth. Thus, the scope's size equals the extreme separation between the telescopes.

Currently international observatories on five continents, including one at the U.S. South Pole Station, are teaming up as the key components of EHT.

The target of EHT is the Milky Way's supermassive black hole known as Sagittarius A* or Sadge-A Star for short. This object, discovered in 1974, cannot be observed in the optical spectrum; this means no human eye can ever see it.

Sage-A* can only be observed in regions of the electromagnetic spectrum that are both far above and below the visible spectrum-these regions include microwaves (above or longer wavelengths) and x-rays and gamma rays (below or shorter wavelengths).

Sadge-A* is a highly active radio source at the bull's eye of our galaxy's core; it is 26,000 light years away from us. From Earth, it is located on the border of the constellations Sagittarius and Scorpius. And just like every galaxy we observe in deep space, our Milky Way has an immense gravity hole at its center.

How big is Sadge-A*? Well, it's big on a mind-numbing scale. The Milky Way's mother of all black holes is estimated to have a mass equivalent to 4 million suns. The stellar mass is compressed into a small volume-and that's essentially what makes the immense "dark star".

Sadge-A*'s event horizon, the boundary around the black hole, is 24 million kilometers (15 million miles) in diameter. It's so large that it is 20 microarcseconds across in the sky or one part per 10 billion of a circle. As seen from Earth, it's approximately the size of one of Apollo 14 astronaut Alan Shepard's golf balls left on the Moon in 1971.

Because the gravity of Sadge-A* bends light, it acts as a giant lens. So when the EHT array finally assembles the data to create an image of Sadge-A*, it will be more of a silhouette of the black hole, not the actual object. And the object will appear larger than it actually is.

Astronomers predict that Sadge-A* will look lopsided due to its hyper spinning; light rays approaching Earth will be brightest when compared to those traveling in the opposite direction.

What's in the Sky: Look for Comet Hartley 2 in the night sky this week. The 6th magnitude comet is visible in binoculars during the evening high in Perseus. On Oct. 20, the comet will be closest to Earth. For an online sky map of the comet's path see: http://www.aerith.net/comet/catalog/0103P/2010.html.

Lou Varricchio, M.Sc. was a science writer at the NASA Ames Research Center. He is a member of the NASA-JPL Solar System Ambassador program in Vermont.